The present invention is related to a color image display apparatus having a frame buffer and a look-up table (LUT), and more particularly to a color image display apparatus in which a single frame buffer is used to display a plurality of types of image data, for example, image data for which a pixel value is specified by an index value of the look-up table, and image data for which it is specified by an RGB (red, green, and blue) value.
In a conventional color image display apparatus, a frame buffer is provided for holding the pixel value of each pixel on a color bit-mapped display screen. Image data are stored once in the frame buffer, and then periodically read out to generate a video signal. The conventional color image display apparatuses are classified into one of two categories depending on the form of the pixel values held in the frame buffer.
A first type of color image display apparatus is one which holds RGR values as the pixel values in the frame buffer. Each of the RGB value has a red value, a green value, and a blue value. A second type of color image display apparatus is one which has a look-up table for holding the RGB values corresponding to each index value and which holds the index values of the look-up table as the pixel values in the frame buffer.
In a computer system having a color image display apparatus, the display area is divided into a plurality of areas, and the images from different image sources are concurrently displayed on the respective display areas. In this case, if all of the image sources specify a pixel value by an RGB value, then a color image display apparatus requires the frame buffer for holding the RGB value. In contrast, if all of the image sources specify a pixel value by an index value of a look-up table, then a color image display apparatus requires the frame buffer for holding the index value.
However, multi-media technology has increased the variety of image sources existing in the same system, and there are both image sources for which a pixel value is specified by an RGB value, and image sources for which a pixel value is specified by an index value of a look-up table.
Under such circumstances, in the color image display apparatus of the type holding an RGB value in the frame buffer, images for which a pixel value is specified by an index value cannot be displayed. Similarly, in the color image display apparatus of the type holding an index value in the frame buffer, images for which a pixel value is specified by an RGB value cannot be displayed.
If two frame buffers are provided so as to combine their outputs, the required frame buffer capacity is doubled. If the specifications of a plurality of image sources are changed to unify their outputs to one of an RGB value and an index value, a substantial specification change of the image sources is required.